Organic polyisocyanates containing allophanate groups and having aliphatically-bound isocyanate groups have already been disclosed, for example in British Patent Specification No. 994,890. According to this Patent Specification, urethane polyisocyanates obtained from simple monohydric or polyhydric alcohols and organic polyisocyanates, in particular diisocyanates, are reacted with further quantities of organic polyisocyanates, preferably diisocyanates, by several hours heating at elevated temperatures or in the presence of catalysts, to form polyisocyanates which contain allophanate groups. A particular disadvantage of this process, apart from the use of catalysts, is that the allophanatization reaction is carried out under conditions of prolonged heating which generally leads to discolored reaction products.
A new process has now surprisingly been found which makes it possible for new organic polyisocyanates containing allophanate groups and having aliphatically or cycloaliphatically bound isocyanate groups to be obtained without the use of catalysts or prolonged heating comparable to that required in the process according to British Patent No. 994,890. The products obtained by the process according to the invention are, therefore, distinguished by their low tinting value and they also have a comparatively low viscosity. They are valuable starting materials for the production of polyurethane resins, particularly for the production of polyurethane lacquers.